Water filter

ABSTRACT

A filter unit for filtering particulates and other foreign matter from a water supply, comprising a filtering chamber. At least a portion of an exterior of the filtering chamber being provided with filtering chamber in use. The mesh being sized to filter particulates and other foreign matter from the water. The filter unit further comprising an outlet through which filtered water exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh. The axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh. The filter unit further comprising a dedicated pump having an inlet communicating with the filtering chamber and an outlet communicating solely with the rotatable member such that operation of the pump causes filtered water from within the filtering chamber to be pumped through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

[0001] The present invention relates to a filter unit for filteringparticulates and other foreign matter from a water supply. In addition,the invention relates to filter unit assemblies and filtration systemsand methods of filtration using the filter unit.

[0002] It is known to provide filter units and filtration systems inwater supplies in order to remove particulate matter and other foreignmatter from the water supply. One example of the use of such a filterunit and filtration system is in filtering the water supply for a fishpond or aquarium.

[0003] It is known to filter a water supply by passing the water supplythrough a small aperture mesh to thereby remove particles and foreignmatter having a diameter greater than the aperture size of the mesh.However, a problem with such a system is that the mesh quickly becomesblocked with the particles and foreign matter removed from the watersupply at which point the filtration system ceases to function and thewater supply is substantially cut-off. It is therefore necessary toregularly clean the meshes of such filtration systems. This processnormally involves dismantling the filtration system which is bothtime-consuming and complicated. In addition, during maintenance of thesystem, the water supply must be cut off.

[0004] GB 2 293 333 proposes one solution to such a problem wherein afiltering chamber is provided surrounded by a small aperture mesh. Wateris drawn through the unit and through the mesh and out of an outlet pipeby means of a pump. A tapping of filtered water from the pumped outletof the filter chamber is then diverted via a return conduit into a backwashing nozzle assembly in the form of a rotatable impeller. The wateris spread from outlets of the impeller against the interior face of themesh in the hope of dislodging particles and debris on the exterior faceof the mesh. However, the device of GB 2 293 333 suffers from a numberof drawbacks. Firstly, the filter is only useable with an activelypumped filtration system. In other words, the filter unit cannot be usedwith a gravity-fed system which is commonly found in larger aquaria andfish ponds. Secondly, in order to produce a sufficient dislodging forceof the water from the impeller, it has been found necessary to divert avery significant proportion of the filtered water from the outlet backinto the rotatable impeller. Potentially up to 90% of the water pumpedthrough the filter unit must be diverted back to the rotatable impeller.Even then, the minimum pore size of the mesh which may be used with sucha filter is restricted to greater than about 250 microns otherwise thepressure drop across the filter unit becomes too great and thevolumetric throughput of the filter unit becomes too low.

[0005] The present invention aims to provide a filter unit whichovercomes the disadvantages of known devices.

[0006] Accordingly, the present invention provides a filter unit forfiltering particulates and other foreign matter from a water supply,comprising a filtering chamber, at least a portion of an exterior of thefiltering chamber being provided with a mesh through which water mayenter the filtering chamber in use, the mesh being sized to filterparticulates and other foreign matter from the water, the filter unitfurther comprising an outlet through which filtered water exits thefilter unit, and a rotatable member located within the filteringchamber, the rotatable member having at least one outlet spaced from aninternal face of a mesh, the axis of rotation of the rotatable memberbeing such that the at least one outlet traverses at least a substantialportion of the internal face of a mesh, the filter unit furthercomprising a dedicated pump having an inlet communicating with thefiltering chamber and an outlet communicating solely with the rotatablemember such that operation of the pump causes filtered water from withinthe filtering chamber to be pumped through the rotatable member to exitthe at least one outlet and impinge on the internal face of the mesh soas to cause particulates and other foreign matter located on an externalface of the mesh to be dislodged.

[0007] The present invention also provides a filter unit assemblycomprising a filter unit as provided above and a tank housing in whichthe filter unit is located, the tank housing being provided with aninlet for entry of water into the tank unit and the outlet of the filterunit forming the outlet of the tank housing.

[0008] The present invention further provides a filtration systemcomprising one or more filter units assemblies as provided above.

[0009] The present invention further provides a method of filteringwater to remove particulates and other foreign matter comprising thesteps of passing the water through a filtering chamber having a meshsized to filter the particulates and other foreign matter from thewater, outputting the water from the filtering chamber through an outletof the filtering chamber, wherein a dedicated pump is used to pump waterfrom the filtering chamber exclusively through a rotatable memberlocated within the filtering chamber to exit through at least one outletof the rotatable member to impinge on an interior face of the mesh so asto dislodge particulates and other foreign matter located on an exteriorface of the mesh.

[0010] The present invention further provides a filtration system forfiltering particulates and other foreign matter from a water supply,comprising a tank with an inlet and an outlet, a filtration unit throughwhich water must pass to reach the outlet, and a sump in whichparticulates and other foreign matter from the water accumulates, thesump having an outlet, a drainage conduit communicating with the outlet,a pump for withdrawing water and accumulated particulates and otherforeign matter through the outlet and discharging it to a drainageconduit, and a programmable controller for operating a valve and pump.

[0011] The present invention further provides a filtration system forremoving particulates and other matter from a water supply, comprising:

[0012] a) foam reactor means;

[0013] b) biological filtration means;

[0014] c) aeration means;

[0015] d) ultraviolet (UV) sterilisation means;

[0016] e) screen filtration means; and

[0017] f) heat exchange means

[0018] mounted one above the next in a tower configuration, wherein thescreen filtration means includes an inlet for receiving water to befiltered, the heat exchange means includes an outlet for deliveringfiltered water and a return conduit connects the foam reactor means tothe heat exchange means such that water passes upwardly through the unitfrom item (e) to item (a) and then downwardly to item (f).

[0019] Embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

[0020]FIG. 1 is a side elevation of a filter unit in accordance with thepresent invention;

[0021]FIG. 2 is a further side elevation of the filter unit of FIG. 1with certain parts omitted for clarity;

[0022]FIG. 3 is a cross-sectional elevation of the filter unit of FIG.1, again with certain parts omitted for clarity;

[0023]FIG. 3a is a cross-sectional elevation of an alternative filterunit, again with certain parts omitted for clarity;

[0024]FIG. 3b is a plan view of the filter unit of FIG. 3a;

[0025]FIG. 4 is a top plan view of the filter unit of FIG. 1, showinghidden components in broken lines;

[0026]FIG. 5 is a cross-sectional detail of part of the filter unit ofFIG. 3;

[0027]FIG. 6 is a cross-sectional detail of another part of the filterunit of FIG. 3;

[0028]FIG. 6b is a cross-sectional detail of an alternative part to thatof FIG. 6;

[0029]FIG. 7 is a cross-section detail of a further part of the filterunit of FIG. 3;

[0030]FIG. 8 is a side elevation of a rotor as used in the filter unitof FIG. 1;

[0031]FIG. 9 is a top plan view of the rotor of FIG. 8;

[0032]FIG. 9a is a top plan view of an alternative rotor;

[0033]FIG. 10 is a perspective view of a detail of the rotor of FIG. 8;

[0034]FIG. 11 is a top plan view of an inlet conduit as used in thefilter unit of FIG. 1;

[0035]FIG. 12 is a cross-sectional side elevation of the inlet conduitof FIG. 11;

[0036]FIG. 13 is a schematic elevation of the filter unit of FIG. 1 in afirst type of tank housing;

[0037]FIG. 13a is a schematic elevation of another filter unit assemblyin accordance with the present invention;

[0038]FIG. 13b is a schematic elevation of another filter unit assemblyin accordance with the present invention;

[0039]FIG. 14 is a schematic elevation of the filter unit of FIG. 1 in asecond type of tank housing;

[0040]FIG. 15 is a schematic elevation of the filter unit of FIG. 1 in athird type of tank housing connected to a biological cleaning stagehousing;

[0041]FIG. 15a is a diagrammatic side view of another embodiment of thepresent invention;

[0042]FIG. 15b is a further embodiment of the present invention;

[0043]FIG. 15c shows the apparatus of FIG. 15a in a gravity-flowfiltration system;

[0044]FIG. 15d shows the apparatus of FIG. 15b in a pumped filtrationsystem;

[0045]FIG. 16 is a schematic elevation of a plurality of the filterunits of FIG. 1 in a vertical stack formation;

[0046]FIG. 17 is a schematic elevation of an alternative tank housing inaccordance with the present invention;

[0047]FIG. 17a is a schematic elevation of an alternative tank housingin accordance with the present invention;

[0048]FIG. 17b is a schematic elevation of another alternative tankhousing in accordance with the present invention;

[0049]FIG. 18 is a schematic cross-sectional view of a filtration unitin accordance with the present invention;

[0050]FIG. 18a is a schematic cross-sectional view of another filtrationunit in accordance with the present invention;

[0051]FIG. 18b is a plan view of a filter media for use in thefiltration unit of FIG. 18;

[0052]FIG. 18c is a side elevation of the filter media of FIG. 18b;

[0053]FIG. 18d is a plan view of the filter media of FIG. 18b in anotherstate;

[0054]FIG. 18e is a plan view of the filter media of FIG. 18 in anotherstate;

[0055]FIG. 18f is a cross-sectional view of another filtration unit inaccordance with the present invention;

[0056]FIG. 18g is a cross-sectional view of part of the filtration unitof FIG. 18g;

[0057]FIG. 19 is a cross sectional view of another filtration unit inaccordance with the present invention; and

[0058]FIG. 20 is a schematic view of a filtration system in accordancewith the present invention.

[0059] Referring to FIGS. 1 to 3, a filter unit 1 in accordance with thepresent invention comprises a filter unit housing 10 having circularupper and lower covers 11, 12. A mesh 13 extends around thecircumference of the filter unit housing 10 extending between the uppercover 11 and lower cover 12. The upper cover 11, lower cover 12 and mesh13 together define a cylindrically shaped filter chamber 9.

[0060] Preferably the materials of the filter unit, except whereotherwise mentioned, are made of stainless steel grade 316.

[0061] An outlet 15 is provided at a centre of the filter chamber 9 inthe lower cover 12. A rubber sleeve 16 located at an end of the outlet15 allows the outlet of the filter chamber 9 to be connected to a pipeor other conduit of varying diameter from approximately 7.5 cm to 15 cm.

[0062] Referring to FIGS. 3 to 7, the mesh 13 is mounted to the uppercover 11 and lower cover 12 by means of tie brackets 33. Each tiebracket 33 comprises an elongated strip of metal having an inturnedflange at either end. The mesh 13 is spot welded to a number of tiebrackets 33. The mesh and tie bracket assembly is then connected to theupper cover 11 and the lower cover 12 by virtue of bolts 28, 26. A‘watertight’ seal is provided by annular seals 20, 27 provided inannular channels 34, 35 formed in the upper cover 11 and lower cover 12respectively. As seen in FIGS. 5 to 7, the mesh 13 protrudes into theupper and lower seals 27, 20 to form an improved connection. As a resultwater can only enter the filter chamber 9 through the mesh 13.

[0063] An alternative seal is illustrated in FIG. 6b wherein the annularchannel is dispensed with. Instead an enlarged gasket or o-ring 20′ isprovided which is sandwiched between the tie bracket 33 and lower cover12 as the bolt 26 is fastened. As a result the O-ring 20 bulges outwardsto form a face seal against the mesh 13. This seal may be used on theupper and lower covers 11, 12.

[0064] The mesh 13 is also made of stainless steel grade 316. Theaperture size of the mesh 13 can be varied depending on the requireddegree of filtration. However, in accordance with the present inventionaperture sizes of 200 microns or less can be utilised. One form of mesh13 is a Hollander weave mesh of aperture size 100 microns. The Hollanderweave construction has been found to offer good resistance to workhardening and fatigue failure. Other mesh types such as wedge wirescreen (also known as triangular bar screen) and plain weaves may beused. The mesh 13 may also be made of nylon of a suitable thickness.

[0065] A rotatable member in the form of a rotor 14 is provided withinthe filter chamber 9 having an axis of rotation which is substantiallyvertical and coincident with the major axis of the cylindrical filterchamber 9. The rotor 14 is mounted to the upper cover 11 and lower cover12 by bolts.

[0066] Referring to FIGS. 8 to 10, the rotor 14 of the filter unit 1comprises a vertically orientated hollow rotor shaft 21 and a hollowrotor arm 22 which extends substantially perpendicular thereto.Preferably, the rotor arm 22 and rotor shaft 21 are welded together. Ateach distal end of the rotor arm 22, there is provided a rotor nozzle23. Each rotor nozzle 23 comprises an outlet 29 which is angled at anangle α (alpha) to a radial direction 36 passing coincident to the rotorarm 22 as shown in FIG. 9. Angle α may be varied substantially 0 and 90degrees. Preferably, a is between 35 and 50 degrees. In one example thetwo outlets 29 are both set with an α of 45 degrees. The two outlets 29may be set at different angles; for example, one outlet may have an α of35 degrees and the other 50 degrees. Alternatively, one of the outletsmay be at 0 degrees and the other outlet at an angle greater than 0degrees.

[0067] Alternatively, as shown in FIG. 9a, the nozzle outlets 29 may beset at 0 degrees and one or more openings 29 a provided in the sidewalls of the nozzle 23 through which a proportion of the water passes inorder to rotate the rotor 14.

[0068] Preferably, the rotor nozzles 23 are also fan-shaped in thevertical dimension as shown in FIG. 8 such that the distal end of eachof the rotor nozzles 23 is wider than the proximal end connected to therotor arm 22. The rotor nozzles 23 may be partially closed across partof its width such that the nozzle outlet at one end of the rotor 14sweeps the upper half of the mesh 13 and the opposite nozzle 23 sweepsthe lower half of the mesh 13. This arrangement has the advantage that alower water pressure is required.

[0069] A pump 17 is provided attached to an exterior of the filter unithousing 10. An inlet of the pump 17 is connected to an interior of thefilter chamber 9 by means of an aperture 32 in the lower cover 12 (asshown in FIG. 4). An outlet of the pump 17 connects solely to the rotor14 via an aperture 31 in the lower cover 12 and an inlet conduit 19. Thepump 17 is consequently dedicated to supplying water to rotor 14.

[0070] The pump 17 is preferably an electric pump powered by an externalpower source. The pump has a rating of greater than 2,000 litres perhour and preferably greater than 4,000 litres per hour. One example of asuitable pump is the ‘Nautilus 6,000’ pump manufactured by Oase having arating of 6,000 litres per hour.

[0071] Referring to FIGS. 11 and 12, the inlet conduit 19 of the filterunit 1 is provided with a first aperture 31 a and a second aperture 30a. When positioned in the filter unit 1, the first aperture 31 acoincides with the aperture 31 in the lower cover 12 which provides aconnection with the outlet of the pump 17. Likewise, the second aperture30 a is coincident with a base of the hollow rotor shaft 21. As such,the outlet of the pump 17 communicates with the interior of the rotor 14via the pump outlet aperture 31, aperture 31 a, internal conduit 19,aperture 30 a and rotor shaft 21.

[0072] An air bleed valve 18 is provided in upper cover 11 to allow airtrapped in the filter unit 1 during installation to be bled off.

[0073] The filter unit 1 is installed in use in a tank housing 40 toform a filter unit assembly. FIG. 13 shows a first type of tank housing40 which comprises an inlet 41 located at or near a top of the tankhousing 40, an outlet pipe 42 and a sump 43 provided with a bottom drainline 44. The filter unit 1 is installed in the tank housing 40 with theoutlet 15 being connected to the outlet pipe 42 by means of the rubbersleeve 16 and a jubilee clip. The tank housing 40 is then filled withwater from inlet 41. During this stage the bleed valve 18 may beoperated to remove any air trapped in the filter unit 1.

[0074] In operation, there is a flow of water from the inlet 41 to theoutlet pump 42 such that the filter unit 1 is surrounded by water to befiltered. Advantageously, locating the inlet 41 at or near the top ofthe tank housing 40 causes an overall movement of water downwardlythrough the tank housing 40 towards filter unit 1 which aids removal ofparticulates and other foreign matter from the mesh 13 and speeds upsettling of the debris in sump 43. In addition, the conical shape of thesump 43 aids downward movement of the debris towards the bottom drainline 44.

[0075] The filter unit assembly may be either gravity-fed or an activelypumped filtration assembly. Either due to the force of gravity or due tothe action of the active pumping, water is passed through the tankhousing 40 and filter unit 1 by entering through mesh 13 and exitingthrough outlet 15 into the outlet pipe 42.

[0076] At the same time, pump 17 is operated to pump water solelythrough rotor 14. The water pumped by pump 17 originates from within thefilter chamber 9 and is therefore free of any particulates or otherforeign matter larger than the aperture size of the mesh 13. Water ispumped into the pump 17 via the inlet aperture 32 in the lower cover 12and pumped out of the pump outlet aperture 31 only into the inletconduit 19 and rotor shaft 21. The pumped water is then forced alongboth arms of the rotor arm 22 and out of the rotor outlets 29 of rotornozzles 23. Due to the angle α of the outlets 29 of the rotor nozzles23, the outflowing water causes the rotor arm 22 to rotate. The wateroutflowing from the rotor outlets 29 is directed against an interiorface of the mesh 13 before passing therethrough. This flow of watercauses particulates and other foreign matter lodged on the outerexterior face of the mesh 13 to be dislodged and to fall away from themesh 13 into sump 43. Periodically the bottom drain line 44 is opened toremove the collected waste material.

[0077] Advantageously, since the flow of water through the rotor 14 isnot taken from the outlet 42, operation of the rotor 14 does not producea decrease in the volumetric flow rate or efficiency of the filter unit1.

[0078] A modified type of tank housing 540 is shown in FIG. 13a in whicha plate, insert or partition 511 is located. The filter unit 1 ispositioned such that its mid-point is level with the partition 511. Anorifice 512 is provided in the partition 511 in which the filter unit 1is located. The partition 511 promotes downward flow within the tankhousing 540 due, in part, to the pressure gradient across the partitiondue to a venturi effect. The downward flow helps the settling of solidsin the sump of the tank housing 540 and also helps prevent the waterbelow the partition 511 being disturbed by the water entering the tankhousing through the inlet. Further, the partition 511 ensures that thewater entering the tank is directed towards the mesh 13 of the filterunit 1 for filtration.

[0079] For maximum efficiency, the radius of the orifice 512 has beenfound to be as follows:

R _(o)={square root}((nr ²+3η)n)

[0080] where

[0081] R_(o)=radius of orifice

[0082] r=radius of filter in centimetres and

[0083] η=flow rate through filter in litres.

[0084] This formula can also be used to determine the radius of the tankhousing in the version shown in FIG. 13, for example.

[0085] Another variant of the tank housing is shown in FIG. 13b. In thisvariant the function of the partition 511 has been incorporated as partof the internal shape of the housing itself. An upper region 515 of thehousing is frusto-conical in shape. A lower region 516 is cylindrical inshape. The junction between the upper region 515 and the lower region516 is located level with the mid-point of the filter unit 1. This hasthe same effect as in the previously described variant of creating apressure gradient which encourages downward flow of water within thetank housing.

[0086] In addition, the tank housing comprises a sump 517 which has amuch reduced cross-sectional area. This has the result of reducing theamount of water which must be emptied fro the tank housing when clearingthe sump 517. In addition, the water exiting the sump 517 into drainline 518 will speed up due to the restriction in diameter. The highvelocities produced ensure that all the collected debris is efficientlyremoved whilst only using a small volume of water.

[0087]FIG. 14 show another type of tank housing 40′ in which the filterunit 1 may be installed. This type of installation occurs typicallywhere an already fitted ‘vortex’ type filter unit is converted tooperate with the filter unit 1 of the present invention. Theinstallation shows how the filter unit 1 may be orientated upside-downwithout impairing performance. The inlet 41′ is also provided with a 90degree elbow pipe 50 to move the effective inlet 51 of the tank housing40′ to at or near the top of the housing. It has been found thatincreased performance of the filter unit 1 occurs where the tank housing40′ is filled in a non-vortex producing manner such that the inflowingwater fills the tank housing 40′ from the bottom up without asignificant water flow in the radial or tangential directions. However,the filter unit 1 may be used in a vortex tank housing.

[0088]FIG. 15 illustrates a third type of tank housing 40″ in which thefilter unit 1 of the present invention may be installed. The outlet 42″of the tank housing 40″ is provided with a secondary pump 54 separatefrom the dedicated pump 17 of the filter unit 1. The secondary pump 54operates to drive water through the tank housing 40″. The figure alsoillustrates how biological filtering or cleaning stages 55 my bearranged in series with the filter unit assembly of the presentinvention to form an integrated filtration system.

[0089]FIG. 15a illustrates a further embodiment according to the presentinvention wherein the filter unit 1 is installed in a tank having a baseand four sidewalls and an open top which is preferably provided with acover 302. The tank is divided into first and second sections 303,305,by a wall 307. The particulate material is removed in the first sectionand the second section contains bio-mass 308 for biologically purifyingthe water. The bio-mass section 308 is itself divided into two sections308 a, 308 b, by a partition wall 306. The first section comprises achamber which receives water to be filtered via an inlet port 309. Thechamber is divided intermediate its upper and lower extremities by apartition wall 311 which has an orifice 313. The lower part of thechamber has a tapered configuration defining a sump 315 at the bottomthereof for the collection of particulate material. A valved outlet 317can be opened to facilitate the removal of particulate material. Thepartition wall is formed by the base of a four sided tray 314 having acontinuous periphery. The tray is preferably removable. The tray fitsinto the upper end of the first section and is supported on a ledge 316.The top edge of the tray allows the water level in the first section tobe higher than that in the second section.

[0090] The filter unit 1, of the type described in the aboveembodiments, opens into the second section 305. The outlet of the filterunit 1 opens into a passageway 323 which opens into the second section305. The filter unit 1 is positioned in the orifice 313 in thepartition. The purposes of this will be described further herein.

[0091] The second section 308 b has an outlet port 331 for filtered andpurified water. It may be provided with a slide valve to control theflow rate and the water level in the two bio-mass compartments 308 a,308 b.

[0092]FIG. 15c illustrates the apparatus of FIG. 15a in conjunction witha pond 330 whose water is to be filtered and purified. In theillustration the tank is connected to the pond 330 by way of a pipeline333 and is positioned such that the level of water in the tank will bedetermined by the level of water W in the pond. A pump 335 generates thecirculation in the system by pumping finally filtered water from theoutlet of the tank back to the pond. In operation water to be filteredenters the first section of the tank and the operation of the pump 335causes water to be drawn through the screen filter unit 1. The waterbelow the partition 311 is relatively calm whereas the water above ismoving. In addition, the positioning of the filter unit 1 within theorifice 313 is such that the water being drawn in generates a pressuredrop between one side of the partition 311 and the other. These factorshave the effect of causing the particulate material which is dislodgedfrom the screen to sink and, in due course, will settle in the sump 315.The removal of particulate material in this manner has the advantagethat particulate material is removed from the pond and yet does notenter the bio-mass and thereby enables a bio-mass to be used which has asmaller particulate size and as a consequence a lesser volume ofmaterial can be used to achieve the same purifying effect.

[0093] Reference is now made to FIG. 15b, which describes a furtherembodiment of filtration apparatus. In this embodiment, removal ofparticulate material is carried out in a catchment tank 450 whichcomprises a modified vortex/cyclone separator. The biological filtermedium is contained in a separate tank 452.

[0094] The vortex separator has an inlet 454 in a sidewall thereof. Theseparator is circular in horizontal section and water is introduced in amanner to set up a swirling motion. The filter separates out largeparticulate material in a manner which is well known and not describedfurther herein. The particulate matter collects in a sump 456 at thebase of the chamber and can be removed by way of a valved outlet 458.

[0095] Water is withdrawn from the chamber via an outlet pipe 460 whichdraws water from the centre of the tank. The inlet to the outlet pipe isprovided with a filter unit 1 of the type described in the aboveembodiments.

[0096] In the illustrated embodiment the rotor 14 is supplied with waterunder pressure from the filtered side of the screen filter. A pump orflow director 466 extracts some of the filtered water and passes italong pipeline 468 to the rotor. As the rotor 14 rotates particulatematerial is displaced from the screen and will sink down into the sump456. The vertical position of the filter unit 1 does not have to belimited to the position shown. It may be closer to the top or lowerdown.

[0097] Water is pumped into the inlet 454 of the vortex separator togenerate the necessary flow velocity and returned to the pond undergravity having passed through the vortex separator 450 and thebiological filter 452. The latter can be of any convenient configurationand is illustrated in FIG. 15b as comprising two sections 475,476separated by a partition 477 and leading over a weir 479 to an outletchamber 481 having an outlet 483. The outlet chamber may incorporateaeration means. A tray 411 in FIG. 15a or similar separator or partitionmay be incorporated.

[0098]FIG. 15d illustrates how either of the apparatus of FIG. 15a or 15b, represented by filter section X shown in dotted outline, could beused in a pumped circulatory system, i.e., where there is no relationbetween the level of water in the pond and the level of water in thefiltration unit.

[0099]FIG. 16 illustrates a further embodiment of the present inventionwherein a plurality of the filter unit assemblies are arranged in avertical stack formation. The outlet 15 of the uppermost filter unit 1is connected to the inlet 41 of the next lowermost tank housing 40 andso on down to the lowermost filter unit 1 whose outlet 15 is connectedto the outlet of the filtration system. Preferably the aperture size ofthe meshes 13 in the filter units 1 decreases down the stack from a meshsize of 100 microns or greater in the uppermost filter unit to a meshsize of 25 microns or less in the lowermost filter unit. In this way aprogressive filtration system is provided.

[0100] Adjacent filter unit assemblies may advantageously be joinedsealingly with one another with the provision of gaskets or O-ring seals60. Of course the successive filter unit assemblies may be arrangedotherwise than in a vertical formation; for example, they may bearranged horizontally where the filtration system is actively pumped.

[0101]FIG. 17 shows a further embodiment of filter unit assembly inaccordance with the present invention. The filter unit assembly 110comprises a tank 112. The tank has an inlet 114 and an outlet 118. Afilter unit 1 is located in the tank. Water entering the tank must passthrough the filtration unit in order to leave the tank 112 through theoutlet 118. A lower portion of the tank forms a sump 120 which taperstowards an outlet 122 and a drainage pipe 124.

[0102] The filter unit 1 may be as described in any of the aboveembodiments. Alternatively, another type of filter unit may be used intank 112.

[0103] A drainage pipe 124 is connected to the outlet 122 of the sump120 and is arranged with an outlet or vent to atmosphere 140 at a levelhigher than the level of the inlet 114 into the tank 112. This ensuresthat the head of water in the drainage pipe 124 is greater than that inthe tank 112. Thus, water entering the tank 112 does not simply drainaway, cutting off supply to the outlet 118.

[0104] However, the outlet 122 from the sump 120 to the drainage pipe124 may also be closed by a valve 134 of any suitable type such as agate valve or ball valve.

[0105] A pump 136 is provided to pump water and accumulated debriswhenever desired (and when the valve 134 is open, if provided) from thesump 120 and along the drainage pipe 124 to waste. The pump may be ofany suitable type which is able to operate without fouling due to thedebris which may be present in the water.

[0106] The valve 134 (if present) and pump 136 are operated by aprogrammable controller 138 which includes a time clock and which can bepreset to activate the valve and pump at desired intervals and for adesired length of time. For example, a conventional domestic centralheating timer can be used.

[0107] The controller can be set to operate the valve 134 and pump 136as often as necessary and for as long as necessary. For example, whenthe system is newly installed and the water to be filtered isparticularly laden with particulates and other foreign matter, it may benecessary to clear the accumulated debris every two hours or so,operating the pump for, say, ten minutes each time. Once this initialfiltration has occurred, ongoing filtration may require a lowerfrequency of perhaps twice a day.

[0108]FIG. 17a shows one variant of tank housing having a sump 120 whichcan be automatically emptied. The emptying of the sump 120 is controlledby the pressure of the dedicated pump 132 of the filter unit 1. Thevalve 134 connected to the drain line 124 is held shut by the waterpressure from the pump 132 via a transfer means 146. The valve 134 canonly open when the pump 132 is switched off. Opening of the valve 134 iscaused by action of a spring 147 located in the valve 134. The switchingof the pump 132 can be controlled by a timing means such as a segmentedtime switch 148.

[0109]FIG. 17b shows an alternative arrangement in which a pump 136 isconnected to the drain point. The operating times of the pump 136 arecontrolled by a timing means such as a segmented time switch 148. Theoutlet of the pump 136 is connected to an upstanding U-bend pipe 149 toprevent drainback of waste water.

[0110] It will be apparent that a number of modifications may be made tothis embodiment without departing from the scope of the invention. Forexample, a different type of filtration unit may be used. A filtrationsystem comprising a number of tanks and filtration units through whichwater passes consecutively may be employed, with each tank including asump and automated discharge system in accordance with the invention.

[0111]FIG. 18 shows another embodiment in accordance with the presentinvention in which a filtration system 210 is built in a towerconfiguration. To facilitate manufacture, installation and maintenancethe system 210 preferably comprises a lower module 212 and an uppermodule 214, releasably attached together at co-operating flanges 216,218, with a seal 220 therebetween.

[0112] The lower module 212 is separated into two chambers by a wall222. The wall 222 is insulated to prevent heat transfer to the catchmenttank 224. The first chamber constitutes a catchment tank 224 which hasan inlet 226 for receiving water to be filtered from a source such as anaquarium or pond. The catchment tank 224 contains a screen filtrationunit 228 for removing particulates above a given size of the typedescribed in the above embodiments. Preferably, the screen filtrationunit 228 is of the type described in any of the embodiments above. Asdescribed above, the dislodged material falls by gravity to accumulatein the bottom of the catchment tank 224 from where it can be removed viaa waste outlet 236.

[0113] To further increase efficiency, the catchment tank 224 includes apartition wall 238 with an orifice in which the screen filtration unit228 is located. This creates a Venturi effect which provides a pressuregradient across the screen 230 which encourages particulate material tomove downwardly in the direction of the reduced pressure and thustowards the bottom of the catchment tank 224.

[0114] The second chamber of the lower module 212, which is locatedbeneath the catchment tank 224, constitutes a heat exchange unit 240.Water which has passed through the screen filtration unit 228, and theother filtration means provided in the upper module 214 as describedfurther below, is returned to the heat exchange unit 240 and passestherethrough in a serpentine-form pipe 242. The pipe 242 may be providedwith a ridged wall to increase the surface area available for heatexchange to take place.

[0115] The heat exchange unit 240 is heated in any convenient manner,for example by a heated gas which is passed into the chamber via a gasinlet 244 for circulation around the pipe 242 and which can be removedvia gas outlet 246 for reheating and recirculation.

[0116] The pipe 242 communicates with a water outlet 248 from where thefiltered and warmed water can be returned to the aquarium or pond.

[0117] The upper module 214 contains further filtration means of varioustypes. Lowermost is an ultraviolet (UV) sterilisation chamber 250. Thischamber receives water which has passed through the screen filtrationunit 228 and illuminates it with UV radiation from a suitable UV source252. The UV radiation kills micro-organisms in the water in a knownmanner.

[0118] Above the UV sterilisation chamber 250, an aeration device suchas an airstone 254 is provided, separated from the UV sterilisationchamber 250 by a perforated partition 250 a. The airstone 254 consistsof a porous material to which air is supplied from an external source256. Preferably the airstone 254 is annular in shape, slightly smallerthan the internal diameter of the upper chamber 214 and located close tothe wall of the upper chamber 214. The air passes through the porousmaterial and bubbles out into the water, preferably in a circularpattern. The airstone 254 forms a partition defining the top of the UVsterilisation chamber 250 and has apertures 258 allowing water to passup into a biological filtration chamber 260. The bubbles aerate thewater and constantly agitate material held in suspension to ensure thatit contacts the biological filter described below. Alternatively, an aircurtain may be used instead of an airstone.

[0119] The biological filtration chamber 260 contains a biologicalfilter 262 which is colonised by bacteria which convert harmful nitrogenbyproducts from aquatic animals into less harmful nitrates.

[0120] The biological filtration chamber 260 contains biological media262 a which is neutrally buoyant and will only work in a system whichhas been filtered sown to 100 microns or less. FIGS. 18b to 18 e showthe properties of the filter media 262 a. The media has a cylindricalbody 290 that is formed from nylon or a similar material and comprises aplurality of fins 291 on its outer surface. The interior of the body 290is divided into four equal quadrants 292 by walls 293. The fins 291 actas a safe area for the beneficial bacteria 294 to grow or colonise butalso act as a cleaning aid by preventing the sticking of any particlesto the media 262 a. The quadrants 292 also allow the bacteria to growand here the bacteria will grow into a ‘bio-film’. Once the bio-film hasdeveloped to a certain thickness as shown in FIG. 18e the complete layerwill fall away from the media 262 a and be removed and passed to waste.

[0121] The bubbles from the airstone 254 move upwardly within the upperchamber 214 whilst remaining near the inner surface of the wall of theupper chamber 214 as shown by the arrows in FIG. 18. The bubbles arethen constrained to move downwardly along the centre line of the upperchamber 214. This has the result of setting up a circulatory flowpattern in the upper chamber 214 which moves the media 262 a of thebiological filter 262 along with it. Consequently the separate particlesof the filter media 262 a collide with one another which has a cleaningeffect.

[0122]FIG. 18a shows an alternative layout of the apparatus in which theairstone 254 has been moved into the central region of the upper chamber214. As shown by the arrows, in this version the circulatory flow in theupper chamber 214 is reversed which has the advantage that the contacttime between the incoming air and filter media 262 a is increased.

[0123] Above the biological filtration chamber 260, at the top of theupper module 214, another form of filtration is provided by a foamreactor 264, also known as a foam fractionator or protein skimmer, whichis separated from the biological filtration chamber 260 by a perforatedpartition 263. The perforations in partitions 250 a and 263 are smallenough to prevent passage of the media 262 a. A foam reactor creates airbubbles which trap organic material at the air-water interface. Thebubbles are forced into a chamber 266 where they burst and deposit theorganic materials which can then be removed via a waste outlet 268. Asis known in the art, such foam reactors 264 remove phosphates, nitrates,nitrites, ammonia and other dissolved solids to reduce the growth ofalgae and blanket weed.

[0124] Clean water exits from the foam reactor 264 via a return pipe 270which returns the water to the heat exchange chamber 240 at the bottomof the unit 210 as described above. Upon exit from the foam reactor 264,a U-bend portion 272 is provided in the return pipe 270. This U-bendportion 272 is rotatable about a substantially horizontal axis as shownto allow the height of water in the foam reactor 264, and the whole unit210, to be controlled.

[0125] In use, water from an aquarium or pond to be cleaned iscirculated through the filtration system 210 by a pump (not shown),entering the system 210 initially through the inlet 226 to the catchmenttank 224. The water passes through the screen filtration unit 228 and isforced upwardly through the UV sterilisation chamber 250, past theairstone 254, through the biological filter 262 and into the foamreactor 264. Having been thoroughly cleaned by these various means, thewater passes through the return pipe 270 to the heat exchange chamber240 to be heated as desired to suit the habitat required in the aquariumor pond. The cleaned and warmed water leaves the system 210 via wateroutlet 248 to be returned to the aquarium or pond.

[0126]FIG. 18f shows a further embodiment having similar components tothe apparatus shown in FIG. 18 but in a different arrangement. Thefiltration system 210 again comprises a filter unit 228 in a catchmenttank 224 which has a wall of varying cross-section as described above inthe above embodiment and shown in FIG. 13b. The bottom of the catchmenttank 224 is provided with a waste outlet 236. Surrounding the catchmenttank 224 is located the biological filtration chamber 260 containing thefilter media 262 a in the level range shown by arrow C in FIG. 18f. Thechamber 260 is located concentric with the catchment tank 224 andpreferably formed as a single unit. An airstone 254 or similar device isprovided towards the base of the biological filtration chamber 260. Adrain 289 is provided to allow emptying, cleaning and refilling of thebiological filtration chamber 260. An auto-level device 400 is providednear a top of the catchment tank 224 the use of which will be describedbelow.

[0127] A water inlet 226 is provided by which water enters near the topof the catchment tank 224. The outlet 216 of the filter unit 228 outputsinto the biological filtration chamber 260 through an anti-media grill280 which prevents the media 262 a passing through into the catchmenttank 224. As described above the bubbles from the airstone 254 and theoutput water from outlet 216 set up a circulatory flow in the biologicalfiltration chamber 260 as shown by the arrows in FIG. 18f.

[0128] Water exits the biological filtration chamber 260 through anoutlet 248 after passing through a second anti-media grill 280 a and isthen passed back to the water source or on to further filtration stagesif necessary.

[0129] As shown in more detail in FIG. 18g the auto-level device 400comprises a water inlet 410 and spaced water outlets 411 at either endof a conduit 414. The conduit 414 is provided with a partition 415 inwhich a valve orifice 413 is located. A float ball 412 which is highlybuoyant is caged in the conduit 414 on the water outlet 411 side of thepartition 415.

[0130] In use the water level in the catchment tank 224 and thebiological filtration chamber 260 are coincident. Where water is pumpedout of outlet 248 of the biological filtration chamber 260 a failure ofthe dedicated pump of the filter unit 228 would lead to the halting ofwater flow into the biological filtration chamber 260 through outlet216. Since the circulatory pump pumping water out of outlet 248 (orgravity in a gravity-fed system) is still operating this can lead to alowering of the water level in the biological filtration chamber 260relative to the water level in the catchment tank 224. Eventually thewater may stop flowing out of outlet 248 leading to damage to thecirculatory pump.

[0131] The auto-level device 400 prevents this. When the water level inthe biological filtration chamber 260 drops below that in the catchmenttank 224 the float ball moves downwardly away from orifice 413 allowingwater to pass through conduit 414 from the catchment tank 224 into thebiological filtration chamber 260. The movement of the ball 412 alsoprovided a visual indication that a problem has developed with thefilter unit 228.

[0132] It will be apparent to those skilled in the art that thisembodiment of the invention provides an improved filtration system whichis compact, space efficient and straight forward to install andmaintain. It will also be apparent that various modifications andalterations to the precise details described may be made withoutdeparting from the scope of the invention as defined by the claims.

[0133]FIG. 19 shows a further embodiment of the present invention inwhich the tank housing 540 is pressurised, in other words the filterunit assembly is part of a closed system which is not open toatmosphere. An air tight lid 545 is provided to seal the filter unitassembly. Alternatively, the tank housing 540 may be made as apressurisable unit. The filter unit 1 and assembly may otherwise be asdescribed in the above embodiments. In particular, the unit 1 may belocated in an orifice formed in a partition 546, and a sump 543 isprovided communicating with a drain line 544. A major advantage of afilter unit assembly which is pressurised is that it may be used in afiltration system that has no loss of head. Such a system is shownschematically in FIG. 20. The output of the filter unit assembly 540inputs into a biological filter stage 560 which then outputs into awater source 570. Water is supplied from the water source 50 to thefilter unit assembly 540 by a circulatory pump 580. Advantageously onlyone pump is required to circulate water round the whole system. Thisdiffers to current systems used in aquaculture where the filtrationstage is non-pressurised. Consequently head is lost at the filtrationstage and therefore another pump is required to move the water throughthe biological filter stage and back to the water source 570.Alternatively, and also disadvantageously, the filtration system has tobe arranged with large vertical displacements between the stages todevelop enough pressure head. The pressurised system of the presentinvention may all be arranged compactly at one level.

[0134] Variations to any of the embodiments described above may be madewithout departing from the scope of the present invention. For example,the filter unit 1 may be provided with a rotor 14 having only a singleoutlet 29 or more than two outlets 29. The pump 17 may be providedremote from the filter unit 1 rather than being attached thereto. In thecase of multiple filter units 1, a single pump 17 may be used to supplywater to all the rotors 14. The mesh 13 has been described as made ofstainless steel. However, other materials such as heavy duty plastic maybe utilised.

[0135] The rating of the dedicated pump 17 may be varied depending onthe aperture size of the mesh 13. For example, it may be preferred touse a pump such as the ‘Oase USP60’.

[0136] Another variation which may be made to the filter unit assembliesof the above embodiments is the provision of a timer switch so as toenable operation of the rotor 14 and pump 17 at periodic intervals asopposed to continuous operation. This has the advantage that theapparatus uses less power. In addition, with the pump 17 switched off,the mesh 13 starts to become blocked by particles in the water. As itdoes so, the effective aperture size of the mesh 13 decreases leading tothe filtration of smaller particles. When the pump 17 is activated thewater from the rotor 14 tends to remove the solids on the mesh 13 in theform of ‘sheets’ which more readily settle out in the sump of the tankhousing than do individual particles. The periodic operation of pump 17is controlled by a switching means such as a simple timer. Moreadvantageously the operation can be controlled by a float switch in thetank housing where the filter unit assembly is actively pumped. As themesh 13 becomes progressively blocked, the water level in the tankhousing starts to rise which eventually triggers the float switch toturn on the pump 17. Where the filter unit assembly is gravity fed, thefloat switch would be situated in a container downstream of the tankhousing. In this case, blockage of the mesh 13 will lead to reduction inthe water level in the downstream container thus activating the floatswitch and pump 17.

[0137] Where the filter unit assembly is pressurised, a pressure switchmay be used as the switching means.

[0138] Advantageously, a switching relay may be used to coordinateoperation of the pump 17 of the filter unit and the circulatory pump ofthe filtration system such that the general circulatory pump is switchedoff when the dedicated pump of the filter unit is switched on. This hasthe advantage that the water exiting the rotor 14 and impinging on themesh 13 does not have to work against an inflow of water through themesh 13.

[0139] Another variation of the filter unit of the present invention isthe use of a dedicated supply of water to the rotor 14 of the filterunit 1. In the embodiments described above, the rotor is supplied withwater by means of dedicated pump 17. Alternatively a different dedicatedsupply may be utilised such as a mains water supply or a source ofotherwise pressurised water. For example, rotor 14 could be plumbed incommunication with a header tank of water having sufficient head toprovide adequate water pressure.

[0140] In a further variation, an impeller may be located in the supplyline which supplies water to the inlet of the catchment tank of thefilter unit assembly. The impeller can then be used to provide themotive force for driving water from within the filter unit 1 into rotor14.

[0141] In a further variation, the rotor may be supplied with adedicated supply of a gas such as air. The gas may be from a compressedgas supply or air powered by an air pump having a rating of 100litres/minute.

[0142] In another variation, the motive force for rotating the rotor 14may be provided by means other than the throughput of fluid though therotor. For example an electric motor may be used or mechanical gearsdriven by the flow of fluid. In this case the nozzles 29 of the rotor donot need to be angled.

[0143] In a further variation, the filter unit 1 may be constructed asshown in FIGS. 3a and 3 b wherein the top cover 11 is removeable simplyby undoing a finger nut 11 a threaded on spindle 21. Once the top cover11 is removed the mesh 13 may be lifted out in one piece for cleaningand/or replacement and the rotor 14 may be accessed.

[0144] Whilst the present invention has been described in detail for usewith aquaria it is to be understood that it applies equally to otherbodies of water which require filtering such as fisheries, hatcheries,swimming pools, baths and ponds in general. In the specific case ofhatcheries which are fed by water drawn from a river source, the filterunit assembly or filtration system may be located at the hatchery or maybe located upstream of the hatchery between the source river and thehatchery.

[0145] Also, the invention may be utilised with other liquids such asblood, plasma, wine, etc. The filter may also be used to filter waterfor irrigation, fisheries, hatcheries, swimming pools, baths and pondsin general.

1. A filter unit for filtering particulates and other foreign matterfrom a water supply, comprising a filtering chamber, at least a portionof an exterior of the filtering chamber being provided with a meshthrough which water may enter the filtering chamber in use, the meshbeing sized to filter particulates and other foreign matter from thewater, the filter unit further comprising an outlet through whichfiltered water exits the filter unit, and a rotatable member locatedwithin the filtering chamber, the rotatable member having at least oneoutlet spaced from an internal face of a mesh, the axis of rotation ofthe rotatable member being such that the at least one outlet traversesat least a substantial portion of the internal face of a mesh, thefilter unit further comprising a dedicated pump having an inletcommunicating with the filtering chamber and an outlet communicatingsolely with the rotatable member such that operation of the pump causesfiltered water from within the filtering chamber to be pumped throughthe rotatable member to exit the at least one outlet and impinge on theinternal face of the mesh so as to cause particulates and other foreignmatter located on an external face of the mesh to be dislodged.
 2. Afilter unit as claimed in claim 1, wherein the pump is located remotefrom the filtering chamber.
 3. A filter unit as claimed in claim 1,wherein the pump is attached to the filtering chamber.
 4. A filter unitas claimed in any preceding claim, wherein the pump has a rating ofgreater than 2,000 litres per an hour, preferably, greater than 4,000litres per hour.
 5. A filter unit as claimed in any preceding claim,wherein the rotatable member has two outlets located at opposite ends ofthe rotatable member.
 6. A filter unit as claimed in claim 5, wherein atleast one of the outlets of the rotatable member is angled at between 0°and 90° of a radial direction passing through the axis rotation of therotatable member.
 7. A filter unit as claimed in claim 6, wherein atleast one of the outlets of the rotatable member is angled at between30° and 50° of a radial direction passing through the axis rotation ofthe rotatable member.
 8. A filter unit as claimed in any precedingclaim, wherein at least one outlet of the rotatable member is angled atsubstantially 90° to a radial direction passing through the axisrotation of the rotatable member.
 9. A filter unit as claimed in claim 7or claim 8, wherein at least one of the outlets of the rotatable memberis angled at substantially 45° to the radial direction.
 10. A filterunit as claimed in any preceding claim wherein means are provided torotate the rotor.
 11. A filter unit as claimed in claim 10 wherein themeans are an electric motor.
 12. A filter unit as claimed in claim 10wherein the means are mechanical gears driven by a flow of fluid.
 13. Afilter unit as claimed in any preceding claim, wherein the mesh has anaperture size of less than 250 microns.
 14. A filter unit as claimed inclaim 13, wherein the mesh has an aperture size of approximately 100microns or less.
 15. A filter unit as claimed in any preceding claim,wherein the mesh is one of a hollander weave mesh, a wedge wire screenor a plain weave.
 16. A filter unit as claimed in any preceding claim,wherein the mesh is made of stainless steel grade
 316. 17. A filter unitas claimed in any of claims 1 to 14 wherein the mesh is made of nylon.18. A filter unit as claimed in any preceding claim, wherein the outletof the pump communicates with a basal portion of the rotatable membervia an inlet conduit.
 19. A filter unit as claimed in any precedingclaim, wherein the outlet of the filter unit comprises a flexible sleevefor attaching the outlet to a pipe or other conduit.
 20. A filter unitas claimed in claim 19, wherein the sleeve is made of rubber or similarmaterial.
 21. A filter unit for filtering particulates and other foreignmatter from a water supply, comprising a filtering chamber, at least aportion of an exterior of the filtering chamber being provided with amesh through which water may enter the filtering chamber in use, themesh being sized to filter particulates and other foreign matter fromthe water, the filter unit further comprising an outlet through whichfiltered water exits the filter unit, and a rotatable member locatedwithin the filtering chamber, the rotatable member having at least oneoutlet spaced from an internal face of a mesh, the axis of rotation ofthe rotatable member being such that the at least one outlet traversesat least a substantial portion of the internal face of a mesh, thefilter unit further comprising a dedicated supply of fluid having anoutlet communicating solely with the rotatable member such that fluid issupplied through the rotatable member to exit the at least one outletand impinge on the internal face of the mesh so as to cause particulatesand other foreign matter located on an external face of the mesh to bedislodged.
 22. A filter unit as claimed in claim 21 wherein thededicated supply of fluid is a source of pressurised water.
 23. A filterunit as claimed in claim 22 wherein the water is pressurised by mainspressure.
 24. A filter unit as claimed in claim 22 wherein the water ispressurised by an impeller.
 25. A filter unit as claimed in claim 22wherein the water is pressurised by a head of water.
 26. A filter unitas claimed in claim 21 wherein the dedicated supply of fluid is a sourceof pressurised gas.
 27. A filter unit as claimed in claim 26 wherein thegas is air.
 28. A filter unit as claimed in claim 27 wherein the air ispressurised by an air pump.
 29. A filter unit assembly comprising afilter unit as claimed in any preceding claim and a tank housing inwhich the filter unit is located, the tank housing being provided withan inlet for entry of water into the tank unit and the outlet of thefilter unit forming the outlet of the tank housing.
 30. A filter unitassembly as claimed in claim 29 wherein water is pumped through the tankhousing by a secondary pump separate from the dedicated pump.
 31. Afilter unit assembly as claimed in claim 29, wherein the inlet isorientated so as to create a vortex of water within the tank housing toaid separation of particulates and other foreign matter.
 32. A filterunit assembly as claimed in claim 31 wherein water is fed by gravitythrough the tank housing.
 33. A filter unit assembly as claimed in anyof claims 29 to 32, wherein the tank housing inlet is located at or neara top of the tank housing.
 34. A filter unit assembly as claimed inclaim 33, wherein the tank housing inlet is provided with an elbow so asto deflect water entering the tank housing into a direction other thanthe radial.
 35. A filter unit assembly as claimed in any of claims 29 to34 wherein the tank housing comprises a sump in which particulatesdislodged from said filter unit accumulate.
 36. A filter unit assemblyas claimed in claim 35 wherein the tank housing has a removeable tray towhich the filter unit is mounted and in which the tray serves topartition the tank housing to define a water inlet section above a baseof the tray and the sump underneath the tray.
 37. A filter unit assemblyas claimed in claim 36 wherein sides of the tray extend above the waterlevel in the tank housing.
 38. A filter unit assembly as claimed in anyof claims 29 to 35 wherein the filter unit is located in an orifice. 39.A filter unit assembly as claimed in claim 38 wherein the radius of theorifice is defined by: R _(o)={square root}((nr ²+3η)/n) whereR_(o)=radius of orifice r=radius of filter in centimetres and η=flowrate through filter in litres.
 40. A filter unit assembly as claimed inany of claims 38 to 39 wherein the orifice is provided in a partitionforming a portion of the tank housing.
 41. A filter unit assembly asclaimed in any of claims 29 to 40 wherein switching means are providedfor enabling periodic operation of the dedicated pump.
 42. A filter unitassembly as claimed in claim 41 wherein the switching means is a timerswitch.
 43. A filter unit assembly as claimed in claim 41 wherein theswitching means is a float switch activatable by the water level in thetank housing.
 44. A filter unit assembly as claimed in claim 41 whereinthe switching means is a float switch activatable by the water level ina container downstream of the tank housing.
 45. A filter unit assemblyas claimed in any of claims 41 to 44 wherein means are provided toinhibit entry of water into the tank unit when the dedicated pump isswitched on.
 46. A filter unit assembly as claimed in claim 45 wherein acirculatory pump of the filtration system is switched off when thededicated pump is switched on.
 47. A filter unit assembly as claimed inany of claims 29 to 46 which is pressurisable.
 48. A filter unitassembly as claimed in claim 47 wherein the tank housing is a pressurevessel.
 49. A filtration system comprising one or more filter unitsassemblies as claimed in any of claims 29 to
 48. 50. A filtration systemas claimed in claim 49, comprising a plurality of filter unit assembliesas claimed in any of claims 29 to 58, wherein the filter unit assembliesare arranged sequentially, wherein the tank housing outlet of eachfilter unit assembly is connected to the tank housing inlet of thesubsequent filter unit assembly or outlet of the filtration system inthe case of the last filter unit assembly.
 51. A filtration system asclaimed in claim 50 wherein the sequential filter unit assemblies arestacked vertically.
 52. A filtration system as claimed in claim 51,wherein a gasket or O-ring seal is provided between adjacent filter unitassemblies.
 53. A filtration system as claimed in any of claims 50 to52, wherein the mesh aperture size of the filter unit in each successivefilter unit assembly decreases in size.
 54. A filtration system asclaimed in claim 53, wherein the mesh aperture size of the first filterunit assembly is 100 microns or greater.
 55. A filtration system asclaimed in any of claims 50 to 54, wherein the mesh aperture size of thelast filter unit assembly is 25 microns or less.
 56. A filtration systemcomprising one or more filter units as claimed in any of claims 1 to 28further comprising one or more biological filtering/cleaning stages. 57.A method of filtering water to remove particulates and other foreignmatter comprising the steps of passing the water through a filteringchamber having a mesh sized to filter the particulates and other foreignmatter from the water, outputting the water from the filtering chamberthrough an outlet of the filtering chamber, wherein a dedicated pump isused to pump water from the filtering chamber exclusively through arotatable member located within the filtering chamber to exit through atleast one outlet of the rotatable member to impinge on an interior faceof the mesh so as to dislodge particulates and other foreign matterlocated on an exterior face of the mesh.
 58. A method as claimed inclaim 57 wherein the water originates from an aquarium, pond, or othervessel holding aquatic life.
 59. A method as claimed in claim 57 orclaim 58 wherein water output through the outlet of the filteringchamber is passed into a biological filtration system.
 60. A method asclaimed in any of claims 57 to 59 wherein the dedicated pump is operatedperiodically.
 61. A method as claimed in claim 60 wherein the dedicatedpump is switched on and off by virtue of the water level in the tankhousing.
 62. A method as claimed in claim 60 wherein the dedicated pumpis switched on and off by virtue of the water level in a containerdownstream of the tank housing.
 63. A filtration system for filteringparticulates and other foreign matter from a water supply, comprising atank with an inlet and an outlet, a filtration unit through which watermust pass to reach the outlet, and a sump in which particulates andother foreign matter from the water accumulates, the sump having anoutlet, a drainage conduit communicating with the outlet, a pump forwithdrawing water and accumulated particulates and other foreign matterthrough the outlet and discharging it to a drainage conduit, and aprogrammable controller for operating a valve and pump.
 64. A filtrationsystem as claimed in claim 63, wherein the outlet from the sump isprovided with a valve.
 65. A filtration system as claimed in claim 64,wherein the valve is a gate valve.
 66. A filtration system as claimed inclaim 64, wherein the valve is a ball valve.
 67. A filtration system asclaimed in any of claims 63 to 66, wherein the controller includes atimer of the type used in central heating systems.
 68. A filtrationsystem as claimed in any of claims 63 to 67, wherein the drainagechannel has an outlet or vent to atmosphere at a higher level than theinlet of the tank.
 69. A filtration system as claimed in any of claims63 to 68, wherein the filtration unit comprises a filtering chamber, atleast a portion of an exterior of the filtering chamber being providedwith a mesh through which water may enter the filtering chamber in use,the mesh being sized to filter particulates and other foreign matterfrom the water, the filter unit further comprising an outlet throughwhich filtered water exits the filter unit, and a rotatable memberlocated within the filtering chamber, the rotatable member having atleast one outlet spaced from an internal face of a mesh, the axis ofrotation of the rotatable member being such that the at least one outlettraverses at least a substantial portion of the internal face of a mesh,the filter unit further comprising a dedicated pump having an inletcommunicating with the filtering chamber and an outlet communicatingsolely with the rotatable member such that operation of the pump causesfiltered water from within the filtering chamber to be pumped throughthe rotatable member to exit the at least one outlet and impinge on theinternal face of the mesh so as to cause particulates and other foreignmatter located on an external face of the mesh to be dislodged.
 70. Afiltration system for removing particulates and other matter from awater supply, comprising: a) foam reactor means; b) biologicalfiltration means; c) aeration means; d) ultraviolet (UV) sterilisationmeans; e) screen filtration means; and f) heat exchange means mountedone above the next in a tower configuration, wherein the screenfiltration means includes an inlet for receiving water to be filtered,the heat exchange means includes an outlet for delivering filtered waterand a return conduit connects the foam reactor means to the heatexchange means such that water passes upwardly through the unit fromitem (e) to item (a) and then downwardly to item (f).
 71. A filtrationsystem as claimed in claim 70, comprising an upper module and a lowermodule releasably joined together, wherein the upper module containsitems (a) to (d) and the lower module contains items (e) and (f).
 72. Afiltration system as claimed in claim 71, wherein the upper and lowermodules are joined by cooperating flanges with sealing meanstherebetween.
 73. A filtration system as claimed in any of claims 70 to72, wherein the screen filtration means comprises a chamber containing ahousing with a screen forming at least one wall of the housing, andmeans located in the housing to exert a back pressure on the screen todislodge particulates from the upstream side of the screen.
 74. Afiltration system as claimed in claim 73, wherein the chamber includes apartition wall having an orifice in which the housing is located, inorder to create a pressure gradient across the screen.
 75. A filtrationsystem as claimed in any of claims 70 to 74, wherein the aeration meanscomprises a porous material supplied with air from an external sourceand wherein the aeration means forms a partition wall between items (b)and (d) with apertures to allow water to pass through.
 76. A filtrationsystem as claimed in any of claims 70 to 75, wherein the return conduitincludes means to control the height of water in the unit.
 77. Afiltration system as claimed in claim 76, wherein the means to controlthe height of water comprises a U-shaped portion of the conduitrotatable about a substantially horizontal axis in use.
 78. A filtrationsystem as claimed in any of claims 70 to 77, wherein the heat exchangemeans comprises a chamber and a heat exchange conduit communicating withreturn conduit and passing through the chamber in a serpentine fashion.79. A filtration system as claimed in claim 78, wherein the heatexchange chamber is heated by circulation of a heated gas.
 80. Afiltration system as claimed in any of claims 70 to 79, furthercomprising pump means to circulate water through the unit.
 81. Afiltration system for removing particulates and other matter from awater supply, comprising: a) biological filtration means; b) aerationmeans; and c) screen filtration means wherein the biological filtrationmeans are arranged concentrically around the screen filtration means.82. A filtration system as claimed in claim 81 wherein means areprovided to maintain equal water levels in the biological filtrationmeans and the screen filtration means.
 83. A filtration system asclaimed in claim 82 wherein the water levelling means comprises a floatball in a conduit moveable into and out of engagement with an orifice torespectively close and open flow of water though said conduit whereinmovement of said float ball is controlled by the level of water in oneof the biological filtration means or the screen filtration means.